Germ cells are remarkable in that, of all the cell types found in an organism they alone retain the ability to give rise to all the embryonic and extra-embryonic cell types that contribute to an organism. This property of totipotency is protected in primordial germ cells (PGCs) by their maintenance of a transcriptionally repressed genome. Two temporally and biochemically distinct mechanisms accomplish this objective in C. elegans. Initially, a C.elegans-specific maternal protein PIE-1, specifically partitioned to the germ line blastomeres, inhibits activation of RNA polymerase. Shortly, after the birth of the PGCs, PIE-1 is degraded and dramatic genome-wide chromatin remodeling occurs to sustain transcriptional repression. However, pathways involved in regulating effectors of global remodeling of the genome remain unknown. A significant goal of this proposal is to uncover molecular mechanisms underlying the specific loss of various marks of 'active'chromatin in newly bom germ cells. The role of RNA polymerase, histone variants and post-translational modifications will be interrogated in the control of these erasure events. Initial experiments also suggest specific activation of histone deacetylase (HDAC) activity at the birth of the primordial germ cells, Z2 and Z3. In complementary approaches, using loss-of-function mutants, RNA interference and transgenic misexpression, the consequence of persistent histone acetylation on the germ-line will be elucidated. Finally, translational and post-translational control of HDAC activity will be probed using genetic and biochemical approaches. Public Health Relevance: These studies address a fundamental question of biomedical relevance: how do embryonic cells, and for that matter, stem cells retain the ability to differentiate into all lineages of the adult animal? The answer to this question will undoubtedly have enormous ramifications for manipulating cells to generate tissue-specific progenitors that could ultimately be used to cure debilitating, degenerative illnesses such as Parkinson's. Additionally, since histone deacetylation has been implicated in aberrant gene silencing in cancerous cells and HDAC inhibitors are being developed as effective anti-cancer drugs, our long-term goal is to utilize our knowledge of histone deacetylation regulation to increase the specificity of next generation epigenetic therapies.